The invention relates to a monitoring system for long term monitoring of concrete pilings and structures, as well as a means of installing and connecting such systems to pilings and structures that have gauges and sensors pre-cast therein.
There is currently no efficient way to communicate information from a concrete structure such as a pile or span, in order to determine conditions related to or generated by installation of such structures. Currently, with concrete structures, such as pilings, that are to be monitored, only approximately one in ten are actually monitored for load bearing and other stress/strain related data due to the significant effort required to manually attach strain gauge/accelerometer monitoring devices to monitor the forces and velocities in the pile during installation. As pilings are generally positioned using choker cables that wrap around the structure that are then lifted by a crane, it is not possible to have anything located on the outside of the piling due to the high risk of it being damaged or cut off by the choker cable during positioning. Currently, after the piling is positioned for driving, the required gauges and sensors are manually attached by climbing to the desired position and attaching them to the standing pile. This is labor intensive, time consuming, costly, and also imposes a safety risk to the installer. As such, only limited monitoring is generally undertaken, resulting in higher design safety factors being required for the structure. A means of performing wireless monitoring at the time of driving would have significant value in reducing the cost and time associated with the testing process, thereby enabling more testing. But there are numerous technical obstacles in doing so, including the wireless transmission of sensor data from the pile.
A basic problem with placing an RF antenna up against, or embedded in concrete is that its performance will be greatly degraded due to the concrete's large dielectric component that varies with the age of the concrete. This presents a very difficult, challenging application environment. With air having a dielectric constant of 1.0, and water 80, concrete varies anywhere from 20 (fresh) to 6 (fully cured after a couple of months depending on water content). The concrete structures in this application are being used about 28 days after cast or sooner, and subsequently were found to have a dielectric constant of about 9.0.
The relatively high dielectric of the concrete placed in close proximity to the RF antenna causes most of the energy emitted from the (now detuned) antenna to be pulled from the antenna and into the concrete. Whatever remaining RF energy coupled to free-air is severely attenuated with distorted and/or erratic patterns, as typical antenna designs are modeled to operate in a free-air environment.
Additionally, after a structural element, such as a pile, is set, no further data is gathered for analysis which could be used for monitoring the long term stability and structural soundness of the structural element in view of cyclic loading and exposure to harsh environments that could cause the structural element to degrade over time, resulting in structural failure.
It would be desirable to provide a more efficient and cost effective method and system for monitoring such concrete structures through the entire useful life of the structure. More preferably, it would be desirable to provide a system that can be easily installed during the casting and manufacturing process which allows monitoring to be done in such a cost effective manner so that all of the concrete structures in a given application, and in particular pilings for buildings, bridges and roadbeds, can be monitored in order to allow for more efficient designs to be utilized without compromising the safety or reliability of the overall structure. Additionally, it would be desirable to provide a system for life-cycle monitoring of such concrete structures, including all concrete structural elements regardless of whether, such as in the case of a piling, the top is cut off after installation. It would also be desirable to provide a means of monitoring embedded gauges regardless of the final state of the structure.